CN116020516A - Graphite-phase carbon nitride photocatalyst with controllable size and preparation method thereof - Google Patents

Abstract

The invention relates to a graphite phase carbon nitride photocatalyst with controllable size and a preparation method thereof, belonging to the technical field of material preparation and photocatalysis. The preparation method comprises the following specific steps: s1, obtaining the original g-C through thermal polymerization of an organic compound precursor ₃ N ₄ The method comprises the steps of carrying out a first treatment on the surface of the S2, the original g-C ₃ N ₄ And uniformly mixing the solvent, performing hydrothermal reaction, and separating and purifying to obtain a mixture of graphite-phase carbon nitride photocatalysts with various sizes. According to the technical scheme, graphite-phase carbon nitride oligomers with the heptazine ring structure can be prepared according to the requirements, and the graphite-phase carbon nitride photocatalyst with the heptazine ring structure is finally prepared through the cooperative coordination of all technological parameters by selecting proper polymerization monomers, solvents and reaction temperature and timeThe preparation process of the ink phase carbon nitride photocatalyst is simple and the size is controllable.

Description

A kind of graphitic carbon nitride photocatalyst with controllable size and preparation method thereof

technical field

The invention belongs to the technical field of material preparation and photocatalysis, and relates to a size-controllable graphite phase carbon nitride photocatalyst and a preparation method thereof.

Background technique

The information disclosed in this background section is only intended to increase the understanding of the general background of the present invention, and is not necessarily taken as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

A series of environmental pollution problems caused by the combustion of fossil fuels have extremely harmful effects on the human living environment, and the energy shortage caused by the non-renewability of fossil fuels has also attracted widespread attention. Renewable energy will play an important role in solving both problems. Solar energy has a series of advantages such as no pollution and large reserves; hydrogen energy has the advantages of high efficiency and renewable energy, and is playing an increasingly important role in replacing fossil fuels. Therefore, semiconductor photocatalysis technology using solar energy to split water to produce hydrogen has broad application prospects.

Graphite phase carbon nitride (gC ₃ N ₄ ) nanomaterials have a suitable bandgap width (2.7eV) and are currently widely used organic semiconductor photocatalysts, but due to the structural defects caused by the pristine gC ₃ N ₄ interlayer stacking Due to the problems of low specific surface area, low transport efficiency of photogenerated carriers, high recombination rate of photogenerated electron-hole pairs, and low utilization rate of visible light, it is difficult to be widely used in the photocatalytic water splitting hydrogen production reaction. However, the special layered structure and suitable bandgap width make it possible to optimize the original gC ₃ N ₄ through various modifications and modifications, overcome the existing shortcomings, and improve its photocatalytic water splitting performance for hydrogen production.

Contents of the invention

In order to improve the serious problem of interlayer stacking of graphite-phase carbon nitride gC ₃ N ₄ , the object of the present invention is to provide a size-controllable graphite-phase carbon nitride photocatalyst and a preparation method thereof. The specific surface area of pristine gC ₃ N ₄ and the transport efficiency of photogenerated carriers were significantly improved by a simple hydrothermal method, and the size of gC ₃ N ₄ was regulated by adjusting the reaction time and temperature.

In order to achieve the above object, the technical solution of the present invention is:

In the first aspect, a method for preparing a size-controllable graphitic carbon nitride photocatalyst, by mixing the original gC ₃ N ₄ material with an organic or inorganic solvent, in the absence of a catalyst, controlling the reaction temperature, time and the type of solvent, a small size carbon nitride photocatalyst with controllable size containing the heptazine ring structure is prepared, thus solving the problem of the low specific surface area of gC ₃ N ₄ containing the heptazine ring structure in the prior art, and the photogenerated carrier Low transmission efficiency, high recombination rate of photogenerated electron-hole pairs, low utilization rate of visible light and other technical problems.

The specific steps are:

S1. Obtain the original gC ₃ N ₄ through thermal polymerization of the organic compound precursor;

S2. Mix the original gC ₃ N ₄ and the solvent evenly, perform hydrothermal reaction, separate and purify to obtain a mixture of graphite-phase carbon nitride photocatalysts of various sizes.

Wherein, in S1, the organic compound precursor is a compound rich in nitrogen and carbon elements, including melamine, urea, dicyandiamide, cyanamide, etc.;

The reaction temperature of the thermal polymerization is 200°C to 600°C;

The original gC ₃ N ₄ is a polymer composed of a plurality of heptazine ring units thermally condensed together, and the microscopic appearance is a massive material with serious stacking and stacking, the specific surface area is small, and the active sites of the reaction are not fully exposed. At the same time, too high polymerization also increases the distance of charge transmission, and the performance of photocatalytic cracking water to produce hydrogen is extremely low;

The heptazine ring structural unit is a structural form that is completely repeated with graphitic carbon nitride (gC ₃ N ₄ ), and is used to describe the structural unit with photocatalytic ability in graphitic carbon nitride (gC ₃ N ₄ );

In S2, the solvent is selected from one or more of water, ethanol, methanol;

The mixing ratio of water and methanol in the solvent is 9:1 to 1:4 by volume;

The reaction temperature is 100°C to 200°C;

The reaction time is 1-10 hours.

Through the hydrothermal method, under the environment of high temperature and high pressure, the rapid and violent movement of solvent molecules will provide a considerable energy shear force. The existence of this shear force will peel off the layered structure of the original gC ₃ N ₄ , and at the same time Promote the breakage of the secondary amine bond between the heptazine ring and the heptazine ring, thereby reducing the size and degree of polymerization of the original gC ₃ N ₄ ; as the size and degree of polymerization decrease, the specific surface area of the exfoliated gC ₃ N ₄ will be significantly increase, the active sites of the reaction are fully exposed, and the reduction of the degree of polymerization will also shorten the distance of charge transmission, further improve the transmission efficiency of photogenerated carriers, and finally improve the performance of the material for photocatalytic water splitting to produce hydrogen; the change of material size will The change of the band gap is caused, and the band gap of gC ₃ N ₄ can be fine-tuned by adjusting the size, thereby providing a suitable band gap for matching with other organic semiconductor materials to form an organic assembly semiconductor photocatalyst. Therefore, through hydrothermal It is simple and effective to modify pristine gC ₃ N ₄ with a low degree of polymerization and controllable size adjustment;

Among them, the longer the hydrothermal reaction time, the higher the temperature, and the higher the boiling point of the selected solvent, the greater the degree of depolymerization of the original g-C3N4 into oligomers, and its corresponding size, photoelectric effect, etc. will increase with the polymerization The degree of degree changes, so organic semiconductor photocatalysts with different sizes of carbon nitride structures can be prepared by selecting appropriate polymerization monomers and reaction conditions.

In the second aspect, the graphite phase carbon nitride photocatalyst prepared by the preparation method of the size-controllable graphite phase carbon nitride photocatalyst.

The beneficial effects of the present invention are:

1. The present invention proposes a method for preparing a graphitic carbon nitride photocatalyst containing a heptazine ring structure with good universality. The original Bulk-C ₃ N ₄ is mixed with a solvent and reacted under certain conditions to obtain The graphite phase carbon nitride photocatalyst containing the heptazine ring structure has mild reaction conditions, the reaction temperature does not exceed 200°C, low cost, and there are many types of polymer monomers to choose from, and is suitable for large-scale production.

2. The preparation method of the present invention is flexible and controllable. By selecting a suitable reaction monomer type, graphite-phase carbon nitride oligomers containing heptazine ring structures of different sizes can be prepared according to needs. Fine-tune the band gap and then form assemblies with other graphitic carbon nitride materials with suitable band gaps.

3. The present invention constitutes an overall technical scheme by selecting suitable polymerized monomers, solvents, reaction temperature and time, and through the synergistic cooperation of various process parameters, and finally prepares a graphite-phase carbon nitride photocatalyst containing a heptazine ring structure , the preparation process of the graphitic carbon nitride photocatalyst is simple and the size is controllable.

Description of drawings

The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations to the present invention.

Fig. 1 is the mechanism schematic diagram of the preparation method of the graphitic phase carbon nitride photocatalyst of size control among the present invention;

Fig. 2 is the infrared spectrogram of the product prepared in Example 1 of the present invention;

Fig. 3 is the XRD spectrogram of the product prepared in Example 1 of the present invention;

Fig. 4 is the infrared spectrogram of the product prepared in Example 2 of the present invention;

Fig. 5 is the XRD spectrogram of the product prepared in Example 2 of the present invention;

Figure 6 is an AFM image of the product prepared in Example 1 of the present invention;

Figure 7 is an AFM image of the product prepared in Example 2 of the present invention;

Figure 8 is an AFM image of the product prepared in Example 3 of the present invention;

Fig. 9 is an AFM image of the product prepared in Example 4 of the present invention.

Figure 10 is a hydrogen evolution diagram of products obtained according to different hydrothermal reaction times in Example 6 of the present invention;

Fig. 11 is a time-peak area diagram of products obtained according to different hydrothermal reaction times in Example 6 of the present invention.

Detailed ways

It should be noted that the following detailed description is exemplary and intended to provide further explanation of the present invention. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It should be noted that the terminology used here is only for describing specific embodiments, and is not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly dictates otherwise, the singular is intended to include the plural, and it should also be understood that when the terms "comprising" and/or "comprising" are used in this specification, they mean There are features, steps, operations, means, components and/or combinations thereof.

In view of the serious problem of interlayer stacking of existing gC ₃ N ₄ , the present invention provides a graphite phase carbon nitride photocatalyst with controllable size and a preparation method thereof.

A typical embodiment of the present invention provides a method for preparing a size-controllable graphite phase carbon nitride photocatalyst, the steps comprising:

S1. Obtain the original gC ₃ N ₄ through thermal polymerization of the organic compound precursor;

S2. Mix the original gC ₃ N ₄ and the solvent evenly, perform hydrothermal reaction, separate and purify to obtain a mixture of graphite-phase carbon nitride photocatalysts of various sizes.

In some embodiments, in S1, the organic compound precursor is a compound rich in nitrogen and carbon elements, including one or more of melamine, urea, dicyandiamide, and cyanamide;

The organic compound precursor is the polymerized monomer of the polymerization reaction of the present invention, and the selection of the polymerized monomer will have a direct impact on the surface morphology, photoelectric properties and size control of the polymer, showing that the selection of the precursor will affect the repeating unit of the polymer Structures such as triazine group and heptazine group. In addition, the choice of different monomers will introduce different functional groups, atoms, etc. to affect its performance. Different monomers will be polymerized to synthesize different shapes such as tubular structure, sheet structure, etc. ;

Preferably, the precursor of the organic compound is melamine; the inventors have found that it is not feasible to use thiourea as the organic compound, because thiourea will react with gases such as oxygen in the air to generate other crystal phase substances when burned in the air;

In some embodiments, in S1, the reaction temperature of thermal polymerization is 200°C-600°C;

In some embodiments, in S2, the solvent is selected from one or more of water, ethanol, methanol;

Preferably, the solvent is water, or a mixture of water and ethanol; the solvent used in the preparation method of the present invention has a great influence on the size control of the product; the inventors have found in experiments that it is not feasible to use ethanol alone as a solvent, because ethanol The saturated vapor pressure is relatively small and cannot provide sufficient shear energy;

In the solvent, the mixing ratio of water and ethanol is a volume ratio of 9:1 to 1:4;

In some embodiments, in S2, the hydrothermal reaction temperature is 100°C-200°C;

Preferably, the hydrothermal reaction temperature is 160-200°C; the reaction temperature will directly affect the air pressure in the reactor, the higher the air pressure, the more vigorous the water molecule will be as a solvent, and the more sufficient shear force will be provided, so the reaction temperature The higher it is, the more favorable it is to control the size of the product;

In some embodiments, in S2, the hydrothermal reaction time is 1-10 hours;

Preferably, the reaction time is 2 to 6 hours, and it takes a certain amount of time to reduce the size of the product, so an appropriate extension of the reaction time is conducive to the formation of smaller-sized products, but when the product has been reduced to a sufficiently small size, the subsequent reaction time The performance improvement of this reaction product has little significance, because this reaction is a depolymerization reaction, and the types of product monomers are different. It is necessary to reasonably control the shape and size of the product by adjusting the reaction time and temperature.

In some embodiments, in S2, the method of cooling and drying in separation and purification is drying or freeze-drying, and the two drying methods do not have much influence on the structure of the product; considering the high recovery rate of samples in the method of freeze-drying , so it is preferably dried by freeze-drying.

As shown in Figure 1, melamine is first placed in an alumina porcelain boat, thermally polymerized in a muffle furnace at a high temperature, and after releasing ammonia, it polymerizes to form a heptazine ring structure, and then releases a heptazine ring structure between the ring heptazine structures Ammonia undergoes further thermal polymerization to form the original gC ₃ N ₄ containing the heptazine ring, and further breaks the CN bond under the action of hydrothermal effect, depolymerizes into an oligomer containing a ring heptazine structure with a lower degree of polymerization, After cooling and drying, a graphite phase carbon nitride photocatalyst with controllable size is obtained;

Among them, the longer the hydrothermal reaction time, the higher the temperature, and the higher the boiling point of the selected solvent, the greater the degree of depolymerization of the original g-C3N4 into oligomers, and its corresponding size, photoelectric effect, etc. will increase with the polymerization The degree of degree changes, so it is possible to prepare organic semiconductor photocatalysts with carbon nitride structures with different sizes by selecting appropriate polymerization monomers and reaction conditions;

The original bulk carbon nitride photocatalyst is a bulk multilayer structure with a size greater than 1 micron. The graphite-phase carbon nitride photocatalyst prepared by the invention is a small-size graphite-phase carbon nitride photocatalyst (small-size gC ₃ N ₄ ). The size of the small-size graphitic carbon nitride photocatalyst is between 2-20nm, which is much smaller than that of the original carbon nitride catalyst. Small-sized features can increase active sites, promote charge separation and transport, improve reactivity, and be more conducive to promoting photocatalytic reaction performance.

Example 1

Put 1 g of melamine in an alumina boat, raise the temperature to 500 ° C in a muffle furnace, and then keep it at a constant temperature for 4 hours to obtain the original gC ₃ N ₄ in the form of a yellow block, and grind the obtained sample into a powder in an agate mortar. Take 50mg of powder sample and transfer it to the polytetrafluoroethylene lining of the autoclave, add 50mL of deionized water, install the hydrothermal reaction kettle and place it in an oven, conduct a hydrothermal reaction at 200°C for 2 hours, and cool to room temperature after the reaction is completed , separated and freeze-dried to obtain the final product.

Fig. 2 and Fig. 3 are respectively the infrared spectrum and the XRD spectrum of the product of embodiment 1, wherein, the absorption bands of 1206cm ^-1 and 1235cm ^-1 and 1316cm ^-1 in Fig. 2 are the characteristic absorption of C-NH-C unit in melamine Peak, belongs to the secondary amine unit of bridging; Among Fig. 3, 13.7 ° with 27.4 ° are respectively gC ₃ N The characteristic absorption peak of ( ₁₀₀ ) and (002) crystal face; This shows, the product of embodiment 1 still has Structural features of gC ₃ N ₄ .

Example 2

Put 1 g of melamine in an alumina boat, raise the temperature to 500 ° C in a muffle furnace, and then keep it at a constant temperature for 4 hours to obtain the original gC ₃ N ₄ in the form of a yellow block, and grind the obtained sample into a powder in an agate mortar. Take 50mg of powder sample and transfer it to the polytetrafluoroethylene lining of the autoclave, add 50mL of deionized water, install the hydrothermal reaction kettle and place it in an oven, conduct a hydrothermal reaction at 200°C for 4 hours, and cool to room temperature after the reaction is complete , separated and freeze-dried to obtain the final product.

Fig. 4 and Fig. 5 are respectively the infrared spectrum and the XRD spectrum of the product of embodiment 2, wherein, the absorption bands of 1206cm ^-1 and 1235cm ^-1 and 1316cm ^-1 in Fig. 4 are characteristic absorptions of C-NH-C units in melamine Peak, belongs to the secondary amine unit of bridging; Among Fig. 5, 13.7 ° with 27.4 ° are the characteristic absorption peaks of (100) and (002) crystal face of g-C3N4 respectively; This shows that the product of embodiment 2 still has gC Structural features of ₃ N ₄ .

Example 3

Put 1 g of melamine in an alumina boat, raise the temperature to 500 ° C in a muffle furnace, and then keep it at a constant temperature for 4 hours to obtain the original g-C3N4 in the form of a yellow block. Grind the obtained sample into a powder in an agate mortar and take Transfer 50mg of powder sample to the polytetrafluoroethylene lining of the autoclave, add 50mL of deionized water, install the hydrothermal reaction kettle and place it in an oven, conduct a hydrothermal reaction at 200°C for 6 hours, cool to room temperature after the reaction is complete, and separate After freeze-drying, the final product was obtained.

Example 4

Put 1 g of melamine in an alumina boat, raise the temperature to 500 ° C in a muffle furnace, and then keep it at a constant temperature for 8 hours to obtain the original g-C3N4 in the form of a yellow block. Grind the obtained sample into a powder in an agate mortar and take Transfer 50mg of powder sample to the polytetrafluoroethylene lining of the autoclave, add 50mL of deionized water, install the hydrothermal reaction kettle and place it in an oven for hydrothermal reaction at 200°C for 6 hours. After the reaction is completed and cooled to room temperature, Freeze-dry after separation to obtain the final product.

Example 5

The products in Examples 1-4 are made into test samples respectively and AFM images are taken, and the obtained results are as shown in Figures 6-9. The white particles in the AFM images represent the graphite phase carbon nitride photocatalyst in the black background. Each embodiment The graphitic phase carbon nitride photocatalysts in all exhibit flake _shape , indicating that the layered structure of pristine _gC3N4 was effectively exfoliated, and the specific surface area of the product was significantly increased. Figure 6 represents: the graphite phase carbon nitride photocatalyst prepared in embodiment 1; Figure 7 represents: the graphite phase carbon nitride photocatalyst prepared in embodiment 2; Figure 8 represents: the graphite phase carbon nitride photocatalyst prepared in embodiment 3 Carbon photocatalyst; Fig. 9 shows: the graphitic phase carbon nitride photocatalyst prepared in embodiment 4; Show that along with the prolongation of reaction time, the size of sample is gradually reducing, realized the controllable preparation of carbon nitride photocatalyst size ;

Because the size is too small, the size of the prepared sample cannot be directly measured by the image, and the software statistics are used to calculate the average value: the size of the graphite phase carbon nitride photocatalyst prepared in Example 1 is about 15nm; the prepared in Example 2 The size of the graphite phase carbon nitride photocatalyst is about 10nm; the size of the graphite phase carbon nitride photocatalyst prepared in Example 3 is about 5nm; the size of the graphite phase carbon nitride photocatalyst prepared in Example 4 is about 3nm;

This embodiment realizes the controllable preparation of gC ₃ N ₄ with a size below 20nm, which can significantly increase active sites, promote charge separation efficiency, and is more suitable for various photocatalytic reactions.

Example 6

According to the preparation method of Example 1, a series of samples were prepared according to the reaction conditions of hydrothermal reaction time of 0h, 1h, 1.5h, 2h, 2.5h, 3h, 4h, and 6h, and their hydrogen evolution ability was tested. The test process is as follows: 25 mg of photocatalyst and 10 mL of triethanolamine (TEOA) are added into 90 mL of ultrapure water as sacrificial electron donors under stirring. Then, aqueous H ₂ PtCl ₆ was added as a precursor of co-catalyst Pt (approximately 3 wt% Pt). Next, the solution was degassed and irradiated with a 300 W xenon lamp equipped with a 420 nm cut-off filter. The photocatalytic _H2 generation rate was determined by using a GC-7900 instrument with a thermal conductivity detector (TCD) and high-purity Ar as the carrier gas. The hydrogen evolution amounts of different samples are shown in Figure 10, and the time-peak area diagrams of different samples are shown in Figure 11. It can be seen from the figure that the hydrogen production effect of the sample with a reaction time of 2 hours is the best.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A preparation method of a size-controllable graphite phase carbon nitride photocatalyst, characterized in that, the specific steps include: S1. Obtain the original gC ₃ N ₄ through thermal polymerization of the organic compound precursor; S2. Mix the original gC ₃ N ₄ and the solvent evenly, perform hydrothermal reaction, separate and purify to obtain a mixture of graphite-phase carbon nitride photocatalysts of various sizes. 2. the preparation method of the graphitic phase carbon nitride photocatalyst with controllable size as claimed in claim 1, is characterized in that, in described S1, organic compound precursor is a kind of compound rich in nitrogen, carbon element, comprises One or more of melamine, urea, dicyandiamide, and cyanamide. 3. The preparation method of the graphite phase carbon nitride photocatalyst with controllable size as claimed in claim 2, characterized in that, preferably, the organic compound precursor is melamine. 4 . The method for preparing the size-controllable graphitic carbon nitride photocatalyst according to claim 1 , characterized in that, in the S1, the reaction temperature of thermal polymerization is 200° C. to 600° C. 5. The preparation method of the graphite-phase carbon nitride photocatalyst with controllable size as claimed in claim 1, characterized in that, in the S2, the solvent is selected from one or more of water, ethanol, and methanol. 6. the preparation method of the graphite phase carbon nitride photocatalyst of controllable size as claimed in claim 5 is characterized in that, solvent is water, or is the mixture of water and ethanol; Preferably, the mixing ratio of water and ethanol is 9:1-1:4 by volume. 7. The method for preparing a graphite-phase carbon nitride photocatalyst with controllable size according to claim 1, characterized in that, in the S2, the hydrothermal reaction temperature is 100°C to 200°C; Preferably, the hydrothermal reaction temperature is 160-200°C. 8. The method for preparing a graphite-phase carbon nitride photocatalyst with controllable size as claimed in claim 1, characterized in that, in the S2, the hydrothermal reaction time is 1 to 10 hours; Preferably, the reaction time is 2-6 hours. 9. The preparation method of the graphitic phase carbon nitride photocatalyst with controllable size as claimed in claim 1, is characterized in that, in described S2, the mode of cooling and drying in separation and purification is drying or lyophilization, preferably freeze dry way. 10. A graphitic phase carbon nitride photocatalyst, is characterized in that, adopts preparation method as described in any one in claim 1-9, the size of the graphitic phase carbon nitride photocatalyst that makes is between 2-20nm between.

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